This application is for a new circular dichroism (CD) spectrometer system, to replace the instrument obtained in 1991 through an NIH Shared Instrumentation Grant. A highly successful shared CD spectroscopy facility has been operating in Robert Wood Johnson Medial School for the past 10 years, under the administration of Dr. Norma Greenfield, an acknowledged expert in this field. The present CD instrument (an Aviv 62 DS provided a cutting edge research tool for studying protein and nucleic acid conformation, stability, and ligand binding to the laboratories of 5 NIH-funded major users, and more than 20 funded minor uses. CD studies from the facility have been included in more than 90 publications. In addition to its research productivity, the CD facility has served as a research-intensive learning environment. Dr. Greenfield has trained more than 100 graduate students, undergraduates, and post-doctoral researchers in the collection, analysis and interpretation of CD spectra of proteins and nucleic acids. For many of these trainees, this was their first exposure to structural biology methodology and analysis. This facility has been funded by user fees, which include 25% of Dr. Greenfield's salary, a service contract, and the nitrogen supply. The continued success of this multi-user facility is endangered. The DOS based computer operating system of the Aviv 62DS CD spectrometer is outdated and its interface boards are incompatible with Pentium computers. The optical performance of this instrument can no longer match that f the new generation of instruments. An Aviv Model 2156 CD instrument is requested in this application, together with a stopped low accessory and several recently developed attachments. This modern instrument and accessories will ensure the continued operation of a successful facility, which supports the research efforts of many funded investigators and complements other available biophysical techniques.